Paper for producing panels and paper-making method

ABSTRACT

The invention relates to a method for making paper, which is characterized in that the paper is impregnated with an acrylate-containing dispersion or mixture and the acrylate-containing dispersion or mixture is forced into the paper. The paper so produced can be used to produce boards, especially floor panels even if said panels have only a mass per unit area of 15 to 35 g/m 2 , thereby reducing the costs of production of such panels.

[0001] The invention relates to a method of making a paper for tiles aswell as a paper produced according to the method. The invention relatesfurther to panels, in the manufacture of which the paper is used, aswell as an associated method of manufacture.

[0002] A tile according the invention can be further processed to form apanel. A panel, for example known from the publication EP 090 6994 A1 isas a rule an elongated thin tile, which can be joined laterally, i.e. atits longer and shorter sides, to further panels, for example throughtongues and grooves. Panels joined together in this way are used inparticular as floor coverings or as wall coverings.

[0003] A tile is produced according to the state of the art, amongstother ways, as follows. A paper impregnated with resin, which is called“counter-pull paper” is prepared. A carrier plate is placed over thecounter-pull paper. A further resin-impregnated paper is arranged abovethe plate. The two papers are pressed together with the plate attemperatures around 200° C. to form the tile.

[0004] The paper which is arranged above the plate is generally providedwith decoration or a pattern which determines the appearance of the tileas viewed from above.

[0005] Particles of SiC or grains of corundum can be rolled onto theside having the decoration before the pressing step, in order to obtaina tile having a particularly resistant surface. In addition a layer ofcellulose is applied to the side having the SiC particles or thecorundum.

[0006] The paper with the printed decoration is called patterned paper.The cellulose layer is identified as “overlay”.

[0007] The patterned paper is arranged with the overlay above thecarrier plate. The patterned paper is then present between the carrierplate and the overlay. Subsequently the counter-pull paper, carrierplate, patterned paper and overlay are pressed together at a temperaturewithin the range of 200° C. When the laminate system is taken from thepress the result is a tile which has on one face a pattern with aparticularly hard surface.

[0008] Panels having the desired dimensions and with lateral tongues andgrooves can be produced from the tiles by sawing and milling. The panelsare used in particular as floor coverings.

[0009] The carrier plate gives the panel mechanical stability. Thedecoration on the patterned paper determines the appearance of thesubsequent wall or floor surface. The layer of corundum or SiC₂ providesgood resistance to abrasion and the like. The counter-pull paper opposesdistortion of the carrier plate. The overlay protects one surface of thepress from the otherwise projecting hard grains of SiC₂ or corundumgrains.

[0010] The papers used in the state of the art generally have a weightabove 70 g per square metre. If the above-mentioned value is notreached, the paper is not sufficiently resistant to tearing in order tobe able to handle the mechanical loads imposed during production of thetiles. The paper is furthermore so thin that it is too transparent to becapable of being used as patterned paper.

[0011] It is true that a high weight of paper has the drawback that theconsumption of material is correspondingly high. In this connection itis not only the actual weight of the paper that has to be taken intoaccount but also the resin with which the paper is impregnated in orderto be able to start the production of a tile. The higher the weight ofthe paper, the more resin is required for impregnating the paper. Thecost of manufacture of the paper is correspondingly increased.

[0012] In order to obtain a thin paper which is resistant to tearing, asynthetic resin mixture is painted onto pre-impregnated paper. Thissynthetic resin mixture does not penetrate the paper but represents anadditional layer which is next to the paper. The underside of the paperis as a rule provided with a self-adhesive layer. The resulting paper isknown under the definition “finish film” and can be stuck onto plates ortiles.

[0013] An aim of the invention is the manufacture and treatment of apaper which is substantially resistant to tearing and in appearance fromthe optical point of view more colour-covering in comparison with thestate of the art stated in the introduction. An aim of the invention isthe production and treatment of economical tiles or plates in which thepaper according to the invention is employed.

[0014] According to the method the paper is impregnated with anacrylate-containing dispersion or mixture. In comparison to animpregnation which is performed only with a resin, the paper impregnatedin accordance with the method is substantially more resistant totearing. The paper can have a weight per unit area of for example 30g/m² and despite this is capable of handling the mechanical loadsimposed in the production of a tile in the manner stated in theintroduction. In fact tests have shown that the mechanical strength ofthe paper according to the invention is so high that the speed ofimpregnation in the resin-impregnation stage provided for production ofthe tiles can be raised from the current 40 to 60 m/min to 120 m/min.Correspondingly small—in comparison with the state of the art cited inthe introduction—is the consumption of the paper material andimpregnating medium.

[0015] The acrylate-containing dispersion or mixture contains water inwhich the acrylate particles are dispersed. Suitable acrylates aretherefore those which have good dispersing qualities.

[0016] In a preferred embodiment of the invention theacrylate-containing dispersion or mixture is pressed into the paper forthe purpose of impregnation. For this purpose the paper is for exampleconducted through rollers which are pressed together. Theacrylate-containing dispersion or mixture is continuously applied to oneroller. When the paper leaves the rollers the dispersion or the mixturehas been pressed into the paper.

[0017] It is important that the dispersed acrylate or the mixture is notsimply painted onto the paper as then the dispersed acrylate or themixture would not have penetrated the paper or would have penetrated itinsufficiently. By the pressing step it is ensured that the dispersionor the mixture penetrates into the paper and so the paper achieves thedesired improved strength. Furthermore the paper is then provided withthe dispersion or the mixture in such a way that during the furthertreatment to produce a tile additionally introduced resin does notpenetrate the paper or at least does so only to a relatively minimumextent.

[0018] In a preferred embodiment of the method the paper is a de-aeratedbefore the acrylate-containing dispersion or mixture is pressed in forimpregnating. For this purpose the paper is steeped in particular on oneside with the acrylate-containing dispersion or mixture. In this way theair present in the paper is replaced by the dispersion or the mixture.

[0019] In one embodiment of the invention a resin-acrylate mixture ordispersion, in particular an amino-resin-acrylate mixture is used forthe impregnation. With such a mixture or dispersion weights of paper toa lower limit of about 15 g per square metre can be achieved. Papersproduced in such a way are, with a suitable mixture ratio, sufficientlyresistant to tearing in order to be able to be employed in theproduction of tiles for example as a printed base paper. It can be leftto the expert in the art to find out suitable mixture ratios byconducting a few tests.

[0020] The paper should not exceed an upper limit of 60 g/m², preferably40 g/m², in order to achieve sufficiently high cost advantages. Optimumvalues currently lie between 25 and 35 g/m².

[0021] In a preferred embodiment of the invention colour pigments, forexample aluminium silicate, calcium carbonate, TiO₂, Al₂O₃ or magnesiumsilicate are added to the mixture. In this way the translucency isgreatly reduced.

[0022] The paper impregnated with the use of colour pigments can be verywell introduced as the patterned paper because of its opacity to lightand high covering ability.

[0023] In one preferred embodiment of the invention theacrylate-containing dispersion or mixture is pressed into the de-aeratedpaper from both sides. It has been found that the paper is then filledout from the middle with the acrylate-containing dispersion or mixture.Such impregnated paper is suitable in a particularly good manner for theproduction of the tiles mentioned in the introduction.

[0024] The paper produced in accordance with the method is distinguishedfrom the finish films in a particular by the fact that the acrylate ispresent in the paper and not simply wholly or largely on the surface.The resistance to delamination is substantially greater than in thefinish films mentioned in the introduction, as steam tests indicate. Inthe steam test paper is exposed to steam for two hours. In conventionalpapers delamination takes place, in contrast to that according to theinvention.

[0025] The paper which is claimed can then be introduced as counter-pullpaper or patterned paper in the production of a tile in the mannerstated in the introduction.

[0026] In one embodiment of the method patterned paper is provided onone side not only with abrasion-resistant particles such as siliconcarbide or corundum particles, but in addition with fibres and/orspheres. The fibres or spheres, in contrast to the abrasion-resistantparticles, comprise soft materials such as polyester, polyamide orglass. The fibres and/or spheres protect a pressing belt from damageduring the pressing of a laminate system which includes the patternedpaper. It is possible to dispense with the provision of an overlay abovea layer of abrasion-resistant particles. In this way it is possible tosave around one third of the costs which are involved in theimpregnation of the patterned paper as well as the application of alayer with the overlay in the state of the art.

[0027] The impregnation of the patterned paper includes in particularthe following steps. The patterned paper is steeped in resin, inparticular amino resin and abrasion-resistant particles are applied toone side having the pattern. Subsequently the fibres and/or spheres areapplied to this. The result is achieved that the fibres and/spheres forma protective covering layer over the abrasion-resistant particles in apress.

[0028] Before the application and of the fibres or spheres the processcan be performed as follows.

[0029] A layer of an amino resin with abrasion-resistant particles in aspecial dispersion is sprayed onto the patterned paper in addition,whereby the final weight per unit area—in relation to the dry weight ofthe raw paper—amounts to 100% to 250%. Spraying on the dispersion hasbeen found to be advantageous, as can be seen from the publication WO00/44984. It is subsequently advantageous to secure the sprayed-ondispersion by smoothing and uniform distribution using rollers.

[0030] The above-mentioned dispersion preferably comprises 100 parts ofan amino resin, 20 to 95 parts of abrasive, and thereforeabrasion-resistant, material, 0.5 to 2.5 parts of a silane adhesionpromoter, 5 to 25 parts of a flow-promoting agent, 0.1 to 0.4 parts of across-linking medium, 0.05 to 0.4 parts of a separating medium and of anamino resin hardener.

[0031] As the amino resin in particular a melamine resin is used, asflow-promoting agent for example polyglycol ether, ε-caprolactam orbutanediol and an abrasive substance, for example silicon carbide havingan average particle size of 60 to 160 μm or aluminium oxide in the formof corundum or out of the melt with a particle size of 60 to 160 μm.Also any desired mixture of silicon carbide and aluminium oxide can beprovided.

[0032] The subsequent application of fibres and/or spheres preferablytakes place as follows. A mixture of a resin with the fibres or thespheres is produced and the mixture is applied to the patterned paper inthe manner described above. The provision of a mixture further improvesthe protection in a press, as then also the additional resin assists inthe protection.

[0033] The thicknesses of the fibres or the diameters of the spheres arepreferably chosen so that during the pressing of a correspondinglaminate system for producing tiles the corundum or silicon carbideparticles are kept away from the corresponding surface of the press. Inthis way damage resulting from hard silicon carbide or corundumparticles is avoided.

[0034] The average diameter of the spheres is preferably greater thanthe average diameter of the fibres when both fibres and spheres areused. The spheres then ensure the desired protective spacing between theabrasion-resistant particles and for example a press belt. The fibres inparticular ensure securing of the resin and oppose the formation oftears.

[0035] The respective active surface of a press is protected by theinvention in an improved and particularly economical manner from damageby abrasion-resistant particles, for example hard corundum or siliconcarbide particles. The maintenance of the active surfaces in a press—forexample a press belt of a so-called double belt laminatinginstallation—takes place at correspondingly longer intervals of time, sothat costs and production down-times associated with the maintenanceschedules are reduced. Overall, significant cost savings are obtained.

[0036] Typical fibre lengths amount to at least 0.5 mm, but preferablyat least a few millimetres, for example 2 mm, 4 mm or 5 mm. The longerthe fibre, the better it is able to protect the surface of a tile fromthe formation of tears. An upper limit on the fibre length is providedin particular by the associated rise in viscosity. In the case of aresin-fibre mixture having too high a viscosity it can no longer beworked. The diameter of the fibres lies for example at a few tens of μmor even 100 μm or more.

[0037] A typical diameter of the spheres lies between 30 and 200 μm.Thereby on the one hand the desired spacing is achieved between thecorundum or silicone carbide particles and a corresponding surface in apress. On the other hand the spheres are small enough not to beperceived by the naked eye.

[0038] The optical impression is not adversely affected by the fibres orspheres if they have the stated sizes and are embedded in the resin.

[0039] The fibres or spheres are preferably made of polyester, polyamideor glass. These materials meet the characteristics which are neededduring production as well as after manufacture. During production theyare sufficiently stable in their behaviour. Polyesters, polyamides orglass are sufficiently soft materials in the sense of the invention inorder to avoid damage to a pressing device. In a finished tile asufficient transparency is given by the stated materials so that theoptical impression of the pattern is not adversely affected. Thematerials preferably make possible relatively large workable fibrelengths which significantly exceed the lengths of fibres made ofcellulose employed according to the invention. The rise in viscositywith increasing fibre length of synthetic polymers such as polyesterfibres, polyamide fibres or glass fibres is in fact small in comparisonwith the increasing fibre lengths of cellulose fibres.

[0040] Accordingly sufficient fibres can be introduced whereby a pressis better protected from damage in comparison with short cellulosefibres. This is particularly the case when the fibres are present in theform of a fleece, as set out further below.

[0041] The fibres and/or spheres can be made of various materials. Thusfor example polyester fibres, polyamide fibres and glass fibres can beemployed equally well.

[0042] Fibres are preferred to spheres as in this way the formation oftears in the surface is avoided. Spheres are therefore preferably usedas a back-up. Accordingly, as spheres preferably use is made of hollowballs of glass for reinforcing the protective action, the balls inparticular having a diameter of 30 to 200 μm for the reasons mentionedabove.

[0043] The patterned paper claimed preferably has a solids contentweight of 25 to 35 g/m². The fibre content then amounts in particular to5 to 100 g/m². In addition for the reinforcement preferably up to 80g/m² of spheres, in particular microglass hollow spheres, are provided.

[0044] In a further preferred embodiment the fibres are present in theform of a fleece. The fibres are so-to-speak woven into one another. Afleece reinforces and protects in a particularly effective manner. Thedanger of the formation of tears is further reduced and thereby thedanger of damage to the respective engaged surface. In the applicationof a resin-fibre mixture the resin is a particularly well secured by thefleece during pressing. The resin then assists particularly well in theprotection in a pressing device.

[0045] In the case where a fleece is provided, the protective action isfurther improved by the introduction of spheres.

[0046] The invention is further explained in conjunction with thefollowing example:

[0047] Paper having a weight of 30 g/m² is moistened on one side with anacrylate-containing dispersion. The dispersion contains the followingcomponents: 770 g of a commercially available acrylate dispersion havinga solids content of 50% by weight, 225 g of a commercially availableurea formaldehyde impregnating resin having a solids content of 50% byweight as well as 5 g of a urea resin hardener. The mixture is finelyagitated and brought into use.

[0048] The moistened paper is conducted through mutuallypressed-together rollers. The rollers have a surface made of hardrubber. The stated dispersion is uniformly applied to the rollers anddistributed uniformly on the surface with the aid of doctor blades.

[0049] The acrylate-containing mixture is present in the interior of thepaper which leaves the rollers. This paper is dried and can subsequentlybe employed for the production of tiles.

[0050] For the production of patterned or decorated paper colourpigments in addition, and in fact 250 g titanium dioxide slurry with asolids content of 70% by weight and 50 g magnesium silicate, are addedto the dispersion. The paper is then at least as opaque as aconventionally produced paper having a weight of 70 g/m².

[0051] The tiles produced using the papers in the manner stated in theintroduction were tested in accordance with EN 438. In this test allstandard norm values were fully met. In particular the steam test wassuccessfully completed.

[0052] The decorated or patterned paper is preferably used in themanufacture of a tile as follows. A mixture of amino resin and corundumparticles is sprayed uniformly on the decorated surface. 15 g/m² ofcorundum is thereby introduced. The now wet paper web is conducted to asuspension drier. A temperature of 170° C. prevails in the drier. Ontothe decorated upper surface of the web which has been thus treated thereis applied in a metered manner a mixture of a commercially availableamino resin and polyester fibres. The solids content of the appliedmaterial amounts to 70 g/m². The fibre content in the mixture is 30% byweight. The average length of the fibres is 5 mm. The mean diameter is80 μm. Subsequently a second drying step is carried out at 160° C.,until the residual moisture content amounts to 7%. The decorated orpatterned paper impregnated in this way is employed further in themanner stated in the introduction, in order to form a tile and inparticular to form a panel for flooring. Likewise paper in accordancewith the invention is used as the counter-pull paper. 150 g/m² of resincan be saved in this way in comparison with the state of the art.However the paper according to the invention also offers advantages overthe state of the art even when he paper weight is very high, amountingfor example to 150 g/m².

1. Method of manufacturing a paper, characterised in that the paper isimpregnated with an acrylate-containing dispersion or mixture.
 2. Methodaccording to claim 1, characterised in that the acrylate-containingdispersion or mixture is pressed into the paper.
 3. Method according toone of the foregoing claims, characterised in that theacrylate-containing dispersion or mixture contains water, in whichacrylate particles are dispersed, and preferably resin, in particular anamino resin.
 4. Method according to one of the foregoing claims,characterised in that colour pigments such as aluminium silicate,calcium carbonate, TiO₂, Al₂O₃ or magnesium silicate are added to theacrylate-containing mixture or dispersion.
 5. Method according to one ofthe foregoing claims, characterised in that the paper is conductedthrough rollers which are pressed together, the acrylate-containingdispersion or mixture being continuously applied to at least one rollerand preferably distributed on the roller with a doctor blade.
 6. Methodaccording to one of the foregoing claims, characterised in that thepaper is de-aerated before the acrylate-containing dispersion or mixtureis pressed into it and for this purpose in particular is steeped on oneside in the acrylate-containing dispersion or mixture.
 7. Methodaccording to one of the foregoing claims, characterised in that thepaper weight amounts to at least 15 grams per square metre and/or doesnot exceed an upper limit of 60 g/m², preferably of 40 g/m².
 8. Methodof manufacturing a tile, in which paper is impregnated in accordancewith one of the foregoing claims and a laminate system which comprisesthe paper and a carrier plate is pressed with the application of heat.9. Method of manufacturing a tile according to the preceding claim, inwhich the laminate system includes a decorated or patterned paper ontowhich a mixture of amino resin and abrasion-resistant particles isapplied, preferably by spraying, before the pressing step.
 10. Method ofmanufacturing a tile according to the preceding claim, in which fibresand/or spheres made of polyester, polyamide or glass are applied to theabrasion-resistant particles before the pressing step.
 11. Papercharacterised by acrylate which is present at least predominantly in theinterior of the paper.
 12. Paper according to the preceding articleclaim, produced in accordance with one of the foregoing method claims.13. Paper according to one of the preceding article claims,characterised by a paper weight of 15 to 60 g/m², preferably up to 40g/m².
 14. Paper according to one of the preceding article claims,characterised by colour pigments which are present in the interior ofthe paper.
 15. Paper according to one of the preceding article claims,characterised in that it displays no delamination on the conclusion ofthe performance of a standardised steam test, in which the paper isexposed to steam for two hours.
 16. Tile, in which the paper accordingto one of the preceding article claims is used.
 17. Tile according tothe preceding claim, in which a surface of the tile is provided withabrasion-resistant particles such as corundum or silicon carbideparticles and preferably with fibres and/or spheres made of polyester,polyamide or glass.
 18. Tile according to one of the two precedingclaims, characterised in that the tile is a flooring panel.